A power supply, sometimes known as a power supply unit or PSU, is a device or system that supplies electrical or other types of energy to a load or group of loads. A power supply, in some embodiments may be configured to convert power in one form to another form, such as converting alternating current (“AC”) power to direct current (“DC”) power. The regulation of power supplies is typically done by incorporating circuitry to tightly control the output voltage and/or current of the power supply to a specific value. The specific value is typically closely maintained despite variations in the load presented to the power supply's output, or any reasonable voltage variation at the power supply's input.
For example, in an electronic device such as a computer, the power supply is typically designed to convert an AC voltage input such as is traditionally provided by a conventional wall socket, into several low-voltage DC power outputs for transmission to the internal components of the electronic device. Conversion may be performed in stages that may include various stage-types such as a rectification stage, a pre-regulation stage such as an active harmonic filter, a regulator/chopper stage, etc. The stages may also be configured to utilize various stage-topologies such as a boost stage, a buck stage, or other derivative topology.
In addition to providing main power outputs to various electronic devices, power supplies are often configured to provide auxiliary and standby power to background systems and sub-systems within an electronic device. For example, even when an electronic device is not fully operational, or is in a standby-mode, power may still be needed to power system clocks, system controllers, system monitors and the like. However, conventional power supplies are often configured to operate with optimal efficiency during normal load conditions, but operate with much less efficiency in low-load conditions. Thus, when an electronic device is operating in a standby mode, or other low-load condition, the efficiency of a power supply may be drastically reduced.
This is especially true in systems that utilize multiple redundant power supplies to provide redundancy protection. It is common practice on equipment that requires high availability to be fitted with multiple redundant power supplies. In systems with multiple redundant power supplies, two or more power supplies may be configured to simultaneously provide redundant power to a load caused by the electronic device. Typically, the redundant power supplies are configured to share the load and to provide power to the load in an efficient manner.
Redundant power supplies are usually sized such that if a power supply fails, the remaining power supplies are capable of supplying power to a load fed by the redundant power supplies. For example, if two power supplies are provided, each will typically have enough capacity to supply the load at full capacity. If three power supplies are provided, in a single fault tolerant system, the power supplies are typically sized so that full power to the load may be supplied by two power supplies. One of skill in the art will recognize other combinations and requirements for providing redundant power supplies.
One of the functions provided by the power supplies is to provide standby power to the electronic device when the device is in a low power state or turned off. In such low power states using conventional power supplies, each of the redundant power supplies continues to supply standby power to the now small load of the electronic device, which results in a large drop in efficiency for each of the redundant power supplies.
In addition, even during normal operation each redundant power supply may be operating at much less than full capacity, which may result in each redundant power supply operating at a lower efficiency than if the power supply was operated at a higher capacity. For example, if two redundant power supplies provide power to a load and each is rated at full load, then if the load never operates at more than full capacity, each power supply will typically supply no more than about 50% of the total load. If the load is operating less than full capacity, for example at 50% load, each of the redundant power supplies may operate at only around 25% of rated capacity. Generally power supplies operate less efficiently at lower loads so systems with redundant power supplies often operate inefficiently.